This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Migrations to the new world brought together individuals from at least three continents. These indigenous and migrant populations inter-mated and subsequently formed new admixed populations, such as African and Latino Americans. These unprecedented events brought together genomes that had evolved independently on different continents for tens of thousands of years and presented new environmental challenges for the indigenous and migrant populations, as well as their offspring. These circumstances provided novel opportunities for natural selection to occur that could be reflected in deviations from the genome-wide ancestry distribution at specific selected loci. Here we present an analysis examining European, Native American and African ancestry based on 284 microsatellite markers in a study of Mexican Americans from the Family Blood Pressure Program. We identified two genomic regions where there was a significant decrement in African ancestry (at 2p25.1, p <10-8 and 9p24.1, p<2x10-5) and one region with a significant increase in European ancestry (at 1p33, p<2 [unreadable] 10-5). We show that these regions are not related to blood pressure. These locations may harbor genes that have been subjected to natural selection in the ancestral mixing of Mexicans.